Chemical synthesis, characterization, and dose optimization of chitosan-based nanoparticles of clodinofop propargyl and fenoxaprop-p-ethyl for management of Phalaris minor (little seed canary grass): First report

Bilal Ahmad Khan; Muhammad Ather Nadeem; Muhammad Mansoor Javaid; Rizwan Maqbool; Muhammad Ikram; Hesham Oraby

doi:10.1515/gps-2022-0096

Article Open Access

Chemical synthesis, characterization, and dose optimization of chitosan-based nanoparticles of clodinofop propargyl and fenoxaprop-p-ethyl for management of Phalaris minor (little seed canary grass): First report

Bilal Ahmad Khan , Muhammad Ather Nadeem , Muhammad Mansoor Javaid , Rizwan Maqbool , Muhammad Ikram and Hesham Oraby

Published/Copyright: December 15, 2022

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From the journal Green Processing and Synthesis Volume 11 Issue 1

Abstract

Phalaris minor is the main and troublesome weed of wheat all over the globe. Chemical weed control is a quick and effective method for weed management. However, herbicides are criticized for environmental pollution and the development of resistance in weeds. Therefore, the present study was planned for chemical synthesis, characterization, and dose optimization of chitosan-based nanoparticles of clodinofop propargyl and fenoxaprop-p-ethyl for the management of Phalaris minor grown in wheat. Chitosan-based nanoparticles of clodinofop propargyl and fenoxaprop-p-ethyl were prepared by the ionic gelification technique. The nanoparticles (NPs) of clodinofop propargyl and fenoxaprop-p-ethyl were sprayed at 3–4 leaf stage of the P. minor weed. Seven different doses (D₀ = weedy check, D₁ = normal herbicide at recommended dose, D₂ = nano herbicide at the recommended dose of normal herbicide, D₃ = 5-fold lower dose of nano herbicide, D₄ = 10-fold lower dose of nano herbicide, D₅ = 15-fold lower dose of nano herbicide, and D₆ = 20-fold lower dose of nano herbicide) were used. Chitosan-based NPs of herbicides were characterized using UV absorbance, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) studies. SEM demonstrated particles in the cluster form with porous structure and the average size ranged from 30 to 60 nm. XRD results confirmed the existence of (2θ) peak at 29.79 related to 160 anatase form in the NPs of clodinofop propargyl and 24.65 related to 76 anatase form in the case of fenoxaprop-p-ethyl. The FT-IR analysis of chitosan-based NPs of both the herbicides perfectly matched the standard parameters. UV-visible spectra exhibited absorption peaks at 300 and 330 nm, for the NPs of fenoxaprop-p-ethyl and clodinofop, respectively. The chitosan-based particles of clodinofop propargyl and fenoxaprop-p-ethyl at the recommended dose of normal herbicide caused 100% mortality and visual injury. However, a 5-fold lower dose of chitosan-based NPs of clodinofop propargyl and fenoxaprop-p-ethyl caused the maximum visual injury (94.00%), mortality (93.75%), minimum chlorophyll contents (7.47%), plant height (cm), fresh biomass (0.27 g), and dry biomass (0.08 g) of P. minor. The chitosan-based NPs of clodinofop propargyl and fenoxaprop-p-ethyl at a 10-fold lower dose of normal herbicides and recommended dose produced a similar effect on the previously mentioned traits of P. minor.

Keywords: Phalaris minor (canary grass); chitosan-based nanoparticles; chlorophyll content; plant height; plant biomass

1 Introduction

Phalaris minor Retz. is the most troublesome and main weed of wheat and other winter crops not only in Pakistan but also in more than 60 countries of the world [1]. Control of this weed is very important to reduce weed–crop competition and increase yield of the wheat crop [2]. Different methods are used to control this including preventive measures as well as biological and chemical methods [3]. Among these methods, chemical control of P. minor was considered the most effective and less time consuming [3]. Frequently, herbicides are applied to the foliar of the targeted plants, which do not kill them entirely but destruct the function and structure of the plant [4]. Fenoxaprop-p-ethyl and clodinofop at a lower dose are responsible for inducing hormesis in narrow leaf weeds such as wild oat and Phalaris minor [5]. They produce a significant effect in decreasing the growth and seed production potential of those weeds. Excessive dependence on clodinofop and fenoxaprop-p-ethyl lead to the development of weed resistance against both the herbicides. Currently, the Phalaris minor weed has developed resistance to herbs in three ways: Acetyl CoA Carboxylase (ACCase), photosynthesis at photosystem II site A, and acetolactate synthase inhibition [3]. Along with resistance, another major problem regarding the chemical herbicide control methods is the injurious effects of herbicides on the environment and crop production. The environmental protection agencies banned many herbicides in the last few decades and there have been reports of resistance to all major herbicide activities [6]. In addition to controlling weed, herbicides also cause harmful effects on living organisms, and reduce soil, water, and air quality [7]. Despite the many side effects of herbicides, their use cannot be obsolete due to their usefulness in increasing crop production to meet the needs of human populations [8]. Thus, to reduce the harmful and adverse effects of herbicides on humans, there is a need of innovative technologies. Nanotechnology is the only technique that help in reducing the dose of herbicide without reducing its efficacy. It is the science of consideration and control of matter at dimensions of roughly 1–100 nm, where unique physical properties make novel applications possible. Its applications have just begun to be used in crop protection after being discovered in pharmacology and medicine. Epitomized and measured release technologies have transformed herbicide utilization. Nanoencapsulation of herbicides in polymeric shells is one of the utmost capable options for reducing the concentration and associated side effects of herbicides applied in the fields. Many problems related to the traditional use of pesticides can be solved and reduced by using nano-engineering. Decomposable and some synthetic polymers are often used for packaging veterinary or pharmaceutical medicines and other active ingredients, but a few studies have described their use as agrochemicals [9]. Herbicides recapitulate can offer controlled release and many other features, such as bioavailability, solubility, risk of oxidation, dissolution, and site-specific targeting [10]. Weed control with nano-capsulated herbicides reduces the herbicide phytotoxicity [11]. Nano-herbicides can control weeds more effectively even at 10-fold lower dose with less or no chances of environmental problems and toxicity to crop plants [12]. It has been reported that the 10-fold lower dose of nano-atrazine produced similar effect on weeds of maize as the commercial atrazine at recommended dose (2,000 g atrazine per hectare) [13].

By using nano-herbicides, there is a great potential to control weeds that are hard to be controlled by the non-nano-herbicides [14,15]. The controlled release of herbicides increases the availability of active ingredients in a desired location for a longer period of time than conventional practices [16]. In agriculture, chitosan have been utilized in several applications to boost plant self-protective mechanisms, plant growth, and frost protection as well as in seed coating, fertilizers, and nutrients [17]. The foremost advantage of the chitosan matrix containing agrochemicals is its capacity to function as a defensive reservoir for the active ingredients, protecting the ingredients from adjacent environment, and monitoring their proclamation which consents them to serve as effective gene delivery systems for plant alteration [18].

Therefore, the present study was planned for the chemical synthesis, characterization, and dose optimization of nanoparticles (NPs) of clodinofop propargyl and fenoxaprop-p-ethyl for the management of P. minor weed growth in wheat crop.

2 Materials and methods

2.1 Collection of weed seeds

The seeds of Phalaris minor grown in wheat crop were collected from the Research area, College of Agriculture, University of Sargodha, Pakistan. The collected seeds were separated, sun-dried, and stored in paper bags at room temperature of 25–35°C.

2.2 Chemical synthesis of chitosan-based NPs of clodinofop propargyl and fenoxaprop-p-ethyl

The NPs were prepared by the ionic gelification technique [19].

2.3 Chemicals used in the study

The following chemicals were used during experimentation: chitosan (MW: 27 kDa, degree of deacetylation: 75–85%), tripoly phosphate, clodinofop propargyl, and fenoxaprop-p-ethyl.

2.4 Characterization of chitosan-based NPs of clodinofop propargyl and fenoxaprop-p-ethyl

Characterization of chitosan-based NPs of clodinofop propargyl and fenoxaprop-p-ethyl can be detected using several high-tech instruments. The size distribution, composition, and morphology of NPs were studied using the Scanning Electron Microscopy (SEM; FEI brand model Inspect S50) in a SEM spot analysis for the validity of nanomaterial. For the determination of the types, the prepared NPs powder was characterized with the help of X-ray diffraction (XRD) (PANalytical X-pert powder, with Cu-Kα as X-ray source). Scanning of the NPs was performed at 2θ with a scan speed of 1°·min⁻¹ and step size of 0.02° [20]. The binding characteristics of NPs were studied using Fourier transform infrared spectroscopy (FT-IR). FT-IR spectroscopy was conducted to explore the functional group sites on the NPs with FT-IR spectrometer (Thermo-Nicolet 6700) using the KBr disk technique [21].

2.5 Herbicidal activity of chitosan-based NPs of clodinofop propargyl and fenoxaprop-p-ethyl

Pot experiments were performed, for optimizing the doses of herbicide NPs, at the Agronomic Research Area, College of Agriculture, University of Sargodha, Pakistan during the winter season of 2020–2021. The experiments were arranged in completely randomized design with a factorial arrangement having three replicates. Ten seeds of P. minor were sown in pots of about seven inches in diameter and ten inches in height and peat moss was used as media for germination. After emergence, eight weed seedlings were maintained per treatment. The NPs of clodinofop propargyl and fenoxaprop-p-ethyl were sprayed at the 3–4 leaf stage of P. minor in 7 different doses (D₀ = weedy check, D₁ = normal herbicide at the recommended dose, D₂ = nano herbicide at the recommended dose of normal herbicide, D₃ = 05-fold lower dose of nano herbicide, D₄ = 10-fold lower dose of nano herbicide, D₅ = 15-fold lower dose of nano herbicide, and D₆ = 20-fold lower dose of nano herbicide). Chlorophyll content was measured 2 weeks after the treatment using the method of Yaxin-1260 [22]. Visual injury (%) and mortality (%) were recorded following ref. [23], and average plant height (cm) of living weed plants was recorded. Fresh biomass (g per pot) of the plants was examined using a digital balance and the average was recorded. After oven drying for 48 h at 70°C, dry biomass (g per pot) was calculated [23].

2.6 Statistical analysis

The collected data were analyzed using Statistics Software (version, 8.1 Statistix, Tallahassee, FL, USA) and the highest significant difference (HSD) test was used to compare the means of treatment at a probability level of 5%.

3 Result and discussion

3.1 Chlorophyll content (%)

Data presented in Table 1 depict that various doses of chitosan-based NPs of clodinofop propargyl and fenoxaprop-p-ethyl significantly affect the chlorophyll content of P. minor compared with control. Chitosan-based NPs showed maximum toxic effect at standard dose of normal herbicide and caused 100% mortality to P. minor. Moreover, with the decrease in dose, the toxic effect of chitosan-based herbicide-loaded NPs reduced and the chlorophyll content increased with a maximum of 45.86% when no chitosan-based nanoparticles were applied. Minimum chlorophyll content (7.75%) was observed with the application of 5-fold lower dose of the NPs. Statistically similar effect on chlorophyll content of P. minor was recorded with the application of conventional herbicides at the recommended dose and 10-fold lower dose of the chitosan-based herbicide-loaded NPs (15.43% and 12.85%, respectively). Chitosan-based NPs of clodinofop propargyl and fenoxaprop-p-ethyl did not differ significantly in their effect on chlorophyll content (%). The maximum chlorophyll content (21.49%) was observed with the application of chitosan-based clodinofop propargyl loaded nanoparticles and the minimum (20.30%) was recorded with the NPs of chitosan-based fenoxaprop-p-ethyl. The interaction effect of various doses of the NPs of the two herbicides were also found to be statistically non-significant. Maximum chlorophyll content (46.03%) was observed under control (0 g dose of fenoxaprop-p-ethyl NPs), while minimum (7.40%) was with the application of 5-fold lower dose of the same NPs. Chlorophyll content is an important parameter for determining the photosynthesis and growth of weed plants.

Table 1

Effect of NPs of clodinofop propargyl and fenoxaprop-p-ethyl on chlorophyll content (%), visual injury (%), and mortality of P. minor

Doses of herbicides	Chlorophyll content (%)			Visual injury (%)			Mortality (%)
Doses of herbicides	Clodinofop propargyl	Fenoxaprop-p-ethyl	Mean value	Clodinofop propargyl	Fenoxaprop-p-ethyl	Mean value	Clodinofop propargyl	Fenoxaprop-p-ethyl	Mean value
D₀	45.70^NS	46.03	45.86A	0.00^NS	0.00	0.00E	0.00^NS	0.00	0.00E
D₁	15.46	15.50	15.43C	79.33	83.67	81.50B	79.16	83.33	81.25C
D₂	No Weed	No Weed	No Weed	100.00	100.00	100.00A	100.00	100.00	100.00A
D₃	8.10	7.40	7.75D	92.33	95.67	94.00A	91.67	95.83	93.75AB
D₄	15.30	10.40	12.85C	79.33	81.00	83.00B	79.16	86.50	82.83BC
D₅	21.33	19.80	20.56B	68.33	69.00	68.67C	66.67	70.83	68.75D
D₆	23.06	22.76	22.91B	58.33	59.67	59.00D	58.33	58.33	58.33D
Mean value	21.49 ^NS	20.30		68.48 ^NS	70.43		67.86	70.69 ^NS
HSD at 5%	Doses = 5.03, Herbicides = ^NS , Doses × herbicides = ^NS			Doses = 9.66, Herbicides = ^NS , Doses × herbicides = ^NS			Doses = 12.25, Herbicides = ^NS , Doses × herbicides = ^NS

D₀ = weedy check, D₁ = normal herbicides at recommended dose, D₂ = NPs of herbicides at the recommended dose of normal herbicide, D₃ = 5-fold lower dose of NPs of herbicides, D₄ = 10-fold lower dose of NPs of herbicides, D₅ = 15-fold lower dose of NPs of herbicides, D₆ = 20-fold lower dose of NPs of herbicides, NS = non-significant.

Mean values in the same column with the same letter do not differ significantly at 5%.

HSD at 5% (mean all the treatments are compared at 5% level of significance).

3.2 Visual injury (%)

Various doses of the chitosan-based NPs of both the herbicides produced a significant effect on the visual injury of P. minor compared with the weedy check (Table 1). Application of chitosan-based NPs at the recommended dose of commercial herbicides resulted in 100% injury to P. minor. With dose reduction, the NPs of chitosan-based herbicides reduced the injury and with no injury (100% alive plants of P. minor) was recorded under control. Application of chitosan-based herbicide NPs at 10-fold lower dose and recommended dose of normal herbicide produced similar effect on visual injury (83.00% and 81.50%, respectively). The NPs of both the chitosan-based herbicides produced statistically non-significant effect on visual injury of P. minor. The interactive effect of both the NPs were also found non-significant. Since the application of NPs of clodinofop propargyl and fenoxaprop-p-ethyl at the recommended dose of normal herbicides resulted in 100% injury compared to control, this may be due to the ACCase-inhibitor effect of herbicides leading to injury symptoms and 100% injury to the weed plants.

3.3 Mortality (%)

Effect of NPs of the two chitosan-based herbicides on the mortality of P. minor weed presented in Table 1 points out that the different doses of NPs significantly affect the mortality of P. minor weed. NPs of herbicides at the recommended dose of normal herbicides resulted in 100% mortality of P. minor. The decrease in dose resulted in reduction in weed mortality with the control presenting 0% mortality. Application of NPs of chitosan-based herbicides at 10-fold lower dose and the recommended dose of normal herbicide produced similar effect on mortality of P. minor (82.83% and 81.25%, respectively). NPs of chitosan-based herbicide fenoxaprop-p-ethyl (70.69%) and clodinofop propargyl (67.86%) did not differ significantly in mortality percentage of P. minor. The interaction effect of NPs of the two herbicides in various doses was also statistically non-significant for mortality. No mortality was observed under control (0%).

3.4 Plant height (cm)

Effect of the NPs of the two herbicides on plant height of P. minor weed presented in Table 2 shows that different doses significantly affect the height. Application of the NPs at the recommended dose of normal herbicides killed all weeds. Thus, no data regarding plant height were recorded. Minimum height (7.47 cm) of P. minor was observed with the application of NPs at 5-fold lower dose of the normal herbicides, while the maximum (19.92 cm) was noticed under control. The effect of the two chitosan-based herbicide NPs did not differ significantly from each other. Taller plants (15.89 cm) and shorter plants (15.80 cm) of P. minor were examined with NPs of clodinofop propargyl and fenoxaprop-p-ethyl, respectively. The interaction effect of different doses of NPs was also found to be non-significant. However, shorter plants (7.40 cm) of P. minor were observed with the application of fenoxaprop-p-ethyl NPs at 5-fold lower dose of normal herbicide, while taller plants (19.92 cm) were observed under control with clodinofop propargyl NPs.

Table 2

Effect of NPs of clodinofop propargyl and fenoxaprop-p-ethyl on plant height (cm), fresh biomass (g), and dry biomass (g) of P. minor

Doses of herbicides	Plant height (cm)			Fresh biomass (g)			Dry biomass (g)
Doses of herbicides	Clodinofop propargyl	Fenoxaprop-p-ethyl	Mean value	Clodinofop propargyl	Fenoxaprop-p-ethyl	Mean value	Clodinofop propargyl	Fenoxaprop-p-ethyl	Mean value
D₀	19.92^NS	19.77	19.96A	6.43	6.33	6.38A	1.18	1.15	1.16A
D₁	15.88	15.76	15.82A	1.31	1.13	1.22C	0.26	0.20	0.23C
D₂	No weed	No weed	No weed	No weed	No weed	No weed	No weed	No weed	No weed
D₃	7.53	7.40	7.47B	0.39	0.16	0.27D	0.11	0.05	0.08C
D₄	15.75	15.61	15.68A	1.25	0.81	1.03C	0.25	0.15	0.20C
D₅	17.03	17.55	17.43A	2.59	2.56	2.57B	0.47	0.40	0.44B
D₆	18.41	19.03	18.72A	3.21	3.04	3.12B	0.51	0.50	0.50B
Mean value	15.89	15.80		2.53	2.34		0.46	0.41
HSD at 5%	Doses = 5.11, Herbicides = ^NS , Doses × herbicides = ^NS			Doses = 0.59, Herbicides = ^NS , Doses × herbicides = ^NS			Doses = 0.20, Herbicides = ^NS , Doses × herbicides = ^NS

Mean values in the same column with the same letter do not differ significantly at 5%.

HSD at 5% (mean all the treatments are compared at 5% level of significance).

3.5 Fresh biomass (g)

The effect of chitosan-based NPs of clodinofop propargyl and fenoxaprop-p-ethyl on fresh biomass is presented in Table 2. Data depicted that the fresh biomass of P. minor was significantly influenced by different doses of chitosan-based herbicide-loaded NPs. Maximum fresh biomass (6.38 g) was recorded with no application of NPs (control), while increase in doses of the NPs resulted in the reduction in fresh biomass. NPs of herbicides at recommended dose of normal herbicides resulted in killing all weeds and minimum fresh biomass (0.27 g) was recorded at 5-fold lower dose of NPs of herbicides. Statistically similar effect on fresh biomass was observed with recommended doses of normal herbicide and 10-fold lower dose of chitosan-based nano-herbicides that was 1.22 and 1.03 g, respectively. NPs of chitosan-based clodinofop propargyl and fenoxaprop-p-ethyl did not differ significantly in their effect on fresh biomass of P. minor. The maximum (2.53 g) and minimum (2.34 g) fresh biomass of P. minor were observed with clodinofop propargyl and fenoxaprop-p-ethyl loaded NPs, respectively. Interactive effect of chitosan-based herbicides loaded NPs and their various doses were also found to be non-significant. 5-fold lower dose of fenoxaprop-p-ethyl loaded nanoparticles produced minimum biomass (0.16 g) of P. minor, while clodinofop propargyl at 0 g produced the maximum (6.43 g).

3.6 Dry biomass (g)

Application of different doses of chitosan-based herbicides loaded NPs produced statistically significant influence on dry biomass of P. minor (Table 2). Application of chitosan based clodinofop propargyl and fenoxaprop-p-ethyl loaded NPs at standard dose of normal herbicides caused 100% P. minor mortality and due to no presence of weeds no data regarding dry biomass were recorded. The reduction in doses of the NPs resulted in decrease in the efficacy of herbicide-loaded NPs. Minimum dry biomass (0.08 g) of P. minor was observed at 5-fold lower dose of chitosan-based herbicide-loaded NPs, while maximum (1.16 g) was observed under control. In this study, the recommended dose of normal herbicides and 10-fold lower dose of herbicides loaded (clodinofop propargyl and fenoxaprop-p-ethyl) NPs produced statistically similar effect on dry biomass (0.41 and 0.39 g, respectively). The influence of herbicides loaded (clodinofop propargyl and fenoxaprop-p-ethyl) NPs was non-significantly different on dry biomass of P. minor. Clodinofop propargyl loaded NPs produced less toxic effect when compared with the fenoxaprop-p-ethyl loaded ones resulting in production of a maximum (0.65 g) and minimum (0.63 g) dry biomass of P. minor, respectively. Interactive effect of the various doses of herbicides loaded NPs were also found to be non-significant.

3.7 SEM

The SEM was used to identify the information regarding the shape and surface morphology of the chitosan-based NPs of clodinofop propargyl (Figure 1) and fenoxaprop-p-ethyl (Figure 2) demonstrated that the shape and surface morphology of the synthesized particles were round and in clustered form with porous structure. This might be due to the presence of toxic chemicals. The NPs were found to be in the size range of 30 and 60 nm, respectively.

Figure 1

SEM micrograph of chitosan-based clodinofop propargyl nanoparticles.

Figure 2

SEM micrograph of chitosan-based fenoxaprop-p-ethyl nanoparticles.

3.8 FT-IR

The physical and chemical compatibilities of the chitosan-based herbicide-loaded nanoparticles of clodinofop propargyl and fenoxaprop-p-ethyl were studied using FT-IR. The FT-IR spectra of clodinofop propargyl of the herbicide-loaded NPs are depicted in (Figure 3). The major functional groups in clodinofop propargyl were in the FT-IR region between 650 and 1,650 cm⁻¹. Free and esterified carboxyl groups were indicated by carbonyl bands in the 655–710 and 930–1,019 cm⁻¹ regions, respectively. The absorption band located at 1,080–1,343 cm⁻¹ was due to the presence of ether, while the band between 1,300 and 1,400 cm⁻¹ was due to the C–C cyclic bonds in the clodinofop propargyl. The broad band from 3,600 to 3,400 cm⁻¹ was due to the polymeric O–H stretching band, while that at 1,600 cm⁻¹ reflected the O–H stretching band of the carboxyl group [24]. On the other hand, the FT-IR spectra of the fenoxaprop-p-ethyl clearly reflected that the major functional groups in clodinofop propargyl were in the FT-IR region between 650 and 1,650 cm⁻¹. Free and esterified carboxyl groups were indicated by carbonyl bands in the 649–778 and 1,018–1,102 cm⁻¹ regions, respectively (Figure 4). The absorption band located at 1,412–1,565 cm⁻¹ was due to the presence of ether, while the band between 1,400 and 1,500 cm⁻¹ was due to the C–C cyclic bonds in the clodinofop propargyl.

Figure 3

FT-IR results of clodinofop propargyl.

Figure 4

FT-IR results of fenoxaprop-p-ethyl.

3.9 UV-visible (UV-Vis) absorption spectrum

UV-Vis absorption spectrum of chitosan-based NPs of clodinofop propargyl and fenoxaprop-p-ethyl is shown in Figures 5 and 6. The maximum absorption peaks of clodinofop propargyl NPs was 330 nm (Figure 5). Meanwhile, the maximum absorption peaks of fenoxaprop-p-ethyl NPs was 300 nm (Figure 6). This distinct signature showed the NPs formation

Figure 5

UV-Vis absorption spectrum of chitosan-based NPs of clodinofop propargyl.

Figure 6

UV-Vis absorption spectrum of chitosan-based NPs of fenoxaprop-p-ethyl.

3.10 XRD analyses

The crystallinity and crystallite size of chitosan-based NPs of clodinofop propargyl and fenoxaprop-p-ethyl were investigated by obtaining the respective XRD patterns. It can be observed that the chitosan-based NPs of clodinofop propargyl exhibited an intensive peak appearing around 2θ value of 27.99° corresponding to the (160) plane of anatase phase (Figure 7). In addition to this peak, several other minor peaks were also observed at 2θ values of 23.58°, 41.47°, 43.73°, and 51.79° corresponding to (108), (65), (58), and (56) planes of anatase phase. In case of chitosan-based NPs of fenoxaprop-p-ethyl, it exhibited an intensive peak around 2θ value of 30.55° corresponding to the (76) plane of anatase phase, and several other peaks were also observed at 2θ values of 20.56°, 24.65°, 28.70° 43.53°, 47.21°, and 56.16° corresponding to (67), (63), (65), (38), (36), and (28) planes of anatase phase (Figure 8).

Figure 7

XRD analyses of chitosan-based NPs of clodinofop propargyl.

Figure 8

XRD analyses of chitosan-based NPs of fenoxaprop-p-ethyl.

4 Discussion

The results of this study demonstrated that the application of NPs of clodinofop propargyl and fenoxaprop-p-ethyl herbicides enhanced the efficacy of herbicides when compared with the commercial herbicides at recommended dose as observed in the complete growth inhibition of P. minor. Similar effect on growth of P. minor was recorded with the application of normal herbicides at recommended dose and 10-fold lower dose of NPs of both the herbicides. The decrease in chlorophyll content of P. minor after the application of clodinofop propargyl and fenoxaprop-p-ethyl loaded NPs may be due to higher activity of the chlorophyll degrading enzyme chlorophyllase, interruption of chloroplast fine structure, and volatility of chloroplast which leads to chlorophyll oxidation and reduction in its concentration in the living plant of P. minor. Similar results were noticed in the application of lower dose of atrazine-loaded nano capsules, which led to a larger reduction in the photosystem II activity than the commercial atrazine formulation at the same concentration in A. viridis and B. pilosa [25]. This study is in line with the results of ref. [26] in which it was reported that the decrease in chlorophyll content after fenoxaprop-p-ethyl application was to be expected due to its assimilation into cell membrane function by physiological processes, such as membrane depolarization. Other researchers [10] revealed that the application of herbicide-loaded NPs controls weeds at lower dose as compared with commercial herbicides.

A greater injury to P. minor was examined with the application of NPs of herbicides at the recommended dose of normal herbicides. However, no injury was recorded under check. Similar effect on injury to P. minor was recorded with the application of normal herbicides at recommended dose and 10-fold lower dose of NPs of both the herbicides. The 100% injury in P. minor after foliar application of the NPs of clodinofop propargyl and fenoxaprop-p-ethyl could be due to membrane depolarization and the retardation of other cell membrane functions [26]. The findings of ref. [10] were in line with these results which depicted that the application of herbicide-loaded NPs controls weeds at lower dose as compared with commercial herbicides. Therefore, herbicide-loaded NPs could be used at lower doses with enhanced effectiveness and less toxicity to the environment.

The 100% mortality of P. minor observed with the application of herbicide-loaded NPs at the recommended dose of normal herbicides may be due to the increased nanosize efficiency in penetrating into the weeds resulting in increased mortality when compared to control. Similar effect on mortality to P. minor was recorded with the application of normal herbicides at recommended dose and 10-fold lower dose of NPs of both the herbicides. The highest weed mortality of 75.91% against P. minor was noted after fenoxaprop-p-ethyl herbicide application [27]. More herbicidal effects of nano-herbicides were reported for metsulfuron methyl, diuron-loaded carboxymethyl, pectin, and metolachlor-loaded NPs compared to non-nano formulations [10,28,29].

It was observed from this study that the height of surviving plants was influenced after their exposure to NPs of herbicides at the recommended dose compared to the normal herbicides. Similar effect on P. minor height was recorded with the application of normal herbicides at recommended dose and 10-fold lower dose of NPs of both the herbicides. This may be due to the reduction in photosynthesis and other plant metabolic processes resulting in lower height of surviving plants as compared to control. These outcomes are also in agreement with ref. [25] which revealed that the 10-fold use of diluted atrazine loaded PCL nanocapsules led to the same repressive results on growth parameters of A. viridis and B. pilosa.

The NPs of herbicides improved the performance of normal herbicides by converting into nanoscale resulting in more charge to mass ratio of herbicides, ultimately increasing penetration and efficacy, and lowering the fresh biomass of P. minor. The use of 10-fold lower dose of nano clodinofop propargyl and fenoxaprop-p-ethyl led to a statistically similar toxic effect against P. minor as the commercial formulation at the standard clodinofop propargyl and fenoxaprop-p-ethyl dose. The findings are supported by ref. [25] in which it was reported that the use of atrazine-loaded PCL nanocapsules at 10-fold lower dose reduced more efficiently shoot and root growth of B. pilosa than commercial atrazine, which ultimately reduced plant biomass. The increased in efficacy of herbicides loaded NPs compared to commercial herbicides have been detected for NPs of diuron, metsulfuron methyl, pectin, and metolachlor and polyethylene glycol [10,28,29].

Various studies [30] supported the round shape and clustered form with porous structure of the synthesized NPs reported in this study (Figures 1 and 2). This might be due to the presence of toxic chemicals. The NPs were found to be in the size range of 30–60 nm, respectively. The broad band from 3,200 to 3,500 cm⁻¹ was due to the polymeric O–H stretching band, while that at 1,600 cm⁻¹ reflected the O–H stretching band of the carboxyl group [24]. The FT-IR spectra of the herbicide-loaded NPs of clodinofop propargyl and fenoxaprop-p-ethyl confirmed the compatible presence of herbicide in the nano formulation. The maximum absorption peaks of NPs clodinofop propargyl was 330 nm. On the other hand, maximum absorption peaks of NPs fenoxaprop-p-ethyl was 300 nm. This distinct signature shows the NPs formation as reported by ref. [21]. Chitosan-based NPs of fenoxaprop-p-ethyl exhibit intensive peak around 2θ value of 30.55° corresponding to the (76) planes of anatase phase and several other peaks are also observed at 2θ values of 20.56°, 24.65°, 28.70°, 43.53°, 47.21°, and 56.16° corresponding to (67), (63), (65), (38), (36), and (28) planes of anatase phase as reported in the literature [30,31,32].

5 Conclusion

Overall, the results of this study revealed that the use of chitosan-based NPs of clodinofop propargyl and fenoxaprop-p-ethyl could be used for 100% control of P. minor. Also, this study examined the same weed control efficacy as from commercial herbicide at a recommended dose and a 10-fold lower dose of chitosan-based NPs of clodinofop propargyl and fenoxaprop-p-ethyl with no chance of environmental pollution. SEM demonstrated that the nano range of particles in cluster form with porous structure and average size range from 30 to 60 nm. XRD results confirmed that the (2θ) peak at 29.79 was related to 160 anatase form in NPs of clodinofop propargyl and in case of fenoxaprop-p-ethyl, 24.65 was related to 76 anatase form. The FT-IR analysis of chitosan-based NPs of both the herbicides perfectly matched the standard parameters. UV–Vis spectra exhibited absorption peaks at 300 and 330 nm, for NPs of fenoxaprop-p-ethyl and clodinofop propargyl, respectively. This study concluded that D₁ = normal herbicide at the recommended dose, D₂ = nano herbicide at the recommended dose of normal herbicide, D₃ = 5-fold lower dose of nano herbicide, D₄ = 10-fold lower dose of nano herbicide, and D₅ = 15-fold lower dose of nano herbicide were found to be effective in the management of P. minor. Therefore, these doses will further be evaluated under the field conditions.

heshamoraby@gmail.com

Acknowledgments

We are really thankful to the Department of Agronomy, College of Agriculture, University of Sargodha-40100, Sargodha for support during research work.

Funding information: The authors would like to thank the Deanship of Scientific Research at Umm Al-Qura University for supporting this work by Grant Code (22UQU4350043DSR04).
Author contributions: Bilal Ahmad Khan: conceptualization, methodology, software, validation, formal analysis, investigation, resources, data curation, writing – original draft preparation, writing – review and editing, and visualization; Muhammad Ather Nadeem: conceptualization, methodology, software, validation, formal analysis, investigation, resources, data curation, writing – original draft preparation, writing – review and editing, visualization, supervision, and project administration; Muhammad Mansoor Javaid: validation, writing – original draft preparation, writing – review and editing, and visualization; Rizwan Maqbool: validation, writing – original draft preparation, writing – review and editing, and visualization; Muhammad Ikram: validation, writing – original draft preparation, writing – review and editing, and visualization; Hesham Oraby: conceptualization, methodology, validation, resources, writing – original draft preparation, writing – review and editing, and visualization.
Conflict of interest: Authors state no conflict of interest.

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Received: 2022-07-19

Revised: 2022-10-13

Accepted: 2022-11-08

Published Online: 2022-12-15

This work is licensed under the Creative Commons Attribution 4.0 International License.

Articles in the same Issue

https://doi.org/10.1515/gps-2022-0096

Keywords for this article

Phalaris minor (canary grass); chitosan-based nanoparticles; chlorophyll content; plant height; plant biomass

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